Effect pigments have also been referred to as gloss pigments, lustrous pigments, pearlescent pigments, or interference pigments. Such pigments having a core consisting of a transparent or nontransparent material are known, such as, for example, natural or synthetic mica, SiO2, aluminum or glass. These cores are coated with a high refractive index material, generally a metal oxide of refractive index greater than about 1.65.
Furthermore, it is possible to obtain pigments that are more intense in color (i.e., having higher chroma) by applying alternating high and low refractive index layers on a substrate.
However, increasing the chroma of effect pigments formed from a platelet diameter (d50) equal to or less than about 15 microns is difficult using alternating high/low refractive index distinct layers. Deposition or co-deposition of a low refractive index distinct layer on the high refractive index layer often leads to agglomeration when the platelet diameter is 15 microns or less.
Thus, it would be useful to develop new ways of making high chroma effect pigments rather than the conventional method of stacking independent and separate alternating high/low refractive index layers on a substrate.